The broad goal of this study is to understand the basic principles that govern actomyosin contractility in non-muscle cells, using C. elegans as a model system. Unlike in skeletal muscle contraction, where force is produced by stable almost crystalline arrays of actin filaments and myosin motors, contractility in non-muscle cells is the global consequence of distributed local force-generating interactions among motors and filaments that rapidly assemble, move and dissemble as they interact. Understanding how organized cell-scale contractile behaviors emerge from these local interactions, and how local regulation of the individual players tunes the same system to produce different behaviors, is fundamental to understanding how cells regulate contractility during normal development and physiology and how it is dysregulated in disease. We will address these challenges in the context of a fundamental and widely used mode of contractility - called focal contractility - in which the periodic assembly, contraction and disassembly of contractile networks drive transient deformations of the cell surface that are rectified to produce cell shape change, cortical flow and tissue deformation. The C. elegans embryo provides a uniquely tractable opportunity to study focal contractility at the surface of single large cells using well-developed tools for molecular genetic manipulation, transgenesis, and high-resolution quantitative light microscopy. We will use a tightly integrated combination of quantitative imaging, experimental manipulations, and predictive computer simulations to ask the following questions: 1) How does the focal contractility cycle work? i.e. what governs the initiation and termination of focal contractions? 2) How is focal contractility regulated by tuning local myosin activity, and the local kinetics of myosin and actin filament assembly and disassembly? 3) Can detailed computer simulations, based on what we know about the properties of and interactions among actin filaments, myosin, crosslinkers and their key regulators, reproduce the macroscopic dynamics of focal contractility and its regulation and reveal the fundamental underlying principles? Given the extensive conservation of molecular players involved in actomyosin contractility, our work will have direct relevance to understanding contractility in many other contexts, both in health and disease.